Technical data

System Management Features

4.13 Volume Shadowing for OpenVMS

This qualiﬁer indicates to the shadowing driver the site location of the

shadow set member or of the shadow set (represented by its virtual unit

name). Prior to using this qualiﬁer, you can deﬁne the site location in the

SYLOGICALS.COM command procedure to simplify its use.

The valid range for nnn is 1 through 255.

The following example shows the site locations deﬁned, followed by the use of

the /SITE qualiﬁer:

$ DEFINE/SYSTEM/EXEC ZKO 1

$ DEFINE/SYSTEM/EXEC LKG 2

$! At the ZKO site ...

$ MOUNT/SYSTEM DSA0/SHAD=($1$DGA0:,$1$DGA1:) TEST

$ SET DEVICE/SITE=ZKO DSA0:

$! At the LKG site ...

$ MOUNT/SYSTEM DSA0/SHAD=($1$DGA0,$1$DGA1) TEST

$ SET DEVICE/SITE=LKG DSA0:

$! At both sites, the following would be used:

$ SET DEVICE/SITE=ZKO $1$DGA0:

$ SET DEVICE/SITE=LKG $1$DGA1:

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/COPY_SOURCE (ddcu:,DSAnnnn:)

Controls whether one or both source members of a shadow set are used as

the source for read data during full copy operations, when a third member

is added to the shadow set. This only affects copy operations that do not use

DCD operations.

HSG80 controllers have a read-ahead cache, which signiﬁcantly improves

single-disk read performance. Copy operations normally alternate reads

between the two source members, which effectively nulliﬁes the beneﬁts of

the read-ahead cache. This qualiﬁer lets you force all reads from a single

source member for a copy operation.

If the shadow set is speciﬁed, then all reads for full copy operations will be

performed from whichever disk is the current ‘‘master’’ member, regardless of

physical location of the disk.

If a member of the shadow set is speciﬁed, then that member will be used

as the source of all copy operations. This allows you to choose a local source

member, rather than a remote master member.

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/ABORT_VIRTUAL_UNIT DSAnnnn:

To use this qualiﬁer, the shadow set must be in mount veriﬁcation. When you

specify this qualiﬁer, the shadow set aborts mount veriﬁcation immediately

on the node from which the qualiﬁer is issued. This qualiﬁer is intended to

be used when it is known that the unit cannot be recovered. Note that after

this command completes, the shadow set must still be dismounted. Use the

following command to dismount the shadow set:

DISMOUNT/ABORT DSAnnnn

System Management Features 4–23